New Deslorelin Formula Improves Pregnancy Rates (AAEP 2011)

A 1.8-mg dose of the deslorelin acetate formulation was safe and effective in inducing ovulation in mares and pregnancy rates for treated mares were similar to those of untreated controls.

Photo: Anne M. Eberhardt/The Horse

The goal in a horse breeding program is to maximize pregnancy rates by breeding mares only once per cycle. Because this is easier said than done, veterinarians employ a little help in a product called deslorelin acetate, which induces ovulation at (or near) the time of breeding. Recently the drug became available in the United States in a slow-release formula, so veterinarians have been determining optimal dosing and timing.

“Implantable formulations of … deslorelin acetate, which mimics the action of a natural ovulation-inducing hormone called gonadotropin-releasing hormone, which are not currently available in the United States, were shown to prolong the interval between ovulation in treated mares,” relayed Edward Squires, MS, PhD, Dipl. ACT, executive director of the University of Kentucky’s Gluck Equine Research Foundation. Squires presented material on the new commercially available FDA-approved deslorelin acetate formulation at the 2011 American Association of the Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas.

In the new formulation (SucroMate) deslorelin acetate is suspended in a sucrose (sugar) solution. To better pinpoint the most efficacious dose of this product for inducing ovulation, Squires and colleague Barry Simon, DVM, administered various doses to research mares and an additional 191 broodmares residing on farms in Australia, Ireland, and the United States. Squires’ and Simon’s key findings included:

A single dose of 1.8 mg/kg deslorelin acetate induced ovulation in 90% of the research mares (that were in estrus and each had a pre-ovulatory egg-containing follicle measuring 30-40 mm on an ovary), a percentage that was markedly higher than with lower doses of the drug;

A single dose of 1.8 mg/kg deslorelin acetate induced ovulation in 77% of the additional 191 broodmares;

When comparing treated and untreated broodmares (in a control group of 97), there was no difference in the interovulatory interval (the number of days between ovulation);

Pregnancy rates did not differ among treated and untreated broodmares; and

All foals born to treated and untreated broodmares were considered normal.

Together, these data show that a 1.8-mg/kg dose of this product was safe and effective in inducing ovulation in mares and pregnancy rates for treated mares were similar to those of untreated controls.

About the Author

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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